1. Field of the Invention
The present invention relates to a remote control system for a vehicle which can automatically lock and unlock the door(s) of a vehicle in wireless communication and more particularly to a remote control system for a vehicle which can automatically lock the door(s) of a vehicle when a user (driver) who carries with him an electronic or entry key (with a portable transmitter/receiver) which includes an identification code assigned to the vehicle walks away a predetermined distance from the vehicle and automatically unlock the same when the user comes back to the distance.
2. Description of the Related Art
Lock/unlock remote-control systems for vehicle doors are known having a so-called, “welcome function”. In the systems, every user (driver) of a vehicle owns an entry key (with a portable transmitter/receiver) which upon receiving a response demand signal that is transmitted from a transmitter installed in the vehicle and is receivable within a predetermined range about the vehicle (which may be referred to as “having a predetermined communication area” hereinafter), can transmit a response signal carrying a unique identification code assigned in advance to each vehicle. When the user walks away from the predetermined range of the vehicle and its entry key is disabled to receive the response demand signal and thus to transmit back the response signal, the door of the vehicle is automatically locked. When the entry key moves into the predetermined range and its response demand signal is received by the transmitter/receiver which then responses thereto to send back a response signal, the door is automatically unlocked.
For example, some of such conventional “welcome function” based lock/unlock remote-control systems for vehicle doors are disclosed in Japanese Patent Laid-open Publications (Heisei)5-106376 and (Heisei)10-25939 in which a transmitter mounted on a vehicle is provided for intermittently transmitting a response demand signal having a predetermined communication area and, when receiving a signal responding to the response demand signal from an entry key which is carried by the user of a vehicle and moves into the predetermined communication area, examining whether the response signal is valid (regular) or not (welcome code examination). When the response signal has been examined to be valid, the door(s) of the vehicle is automatically unlocked. On the contrary, when the response signal is not valid or when the entry key stays out of the predetermined communication area and the vehicle-mounted transmitter receives no response signal, the door remains locked.
Accordingly, when the user of the vehicle carrying the entry key simply walks away from the predetermined range of the vehicle, the door of the vehicle can automatically be locked without paying any attention to or operating the entry key. When the user comes into the range, the door can automatically be unlocked. This requires no boresome actions of unlocking the door for riding the vehicle as well as contributes to the prevention of failing to lock door(s), and of vehicle theft.
The conventional systems have some advantages, particularly once the communication area is preset to a smaller size (for example, one meter in radius), the systematic locking of the door can easily be confirmed after getting off the vehicle, the power consumption for transmitting signals can be as small as not hostile to a battery, and the ID code (uniquely assigned to a vehicle) can hardly be intercepted by any other parties. The locking of the door may be easily confirmed by auditorily and visually perceiving the sound of a door locking mechanism and the shift of an inside door lock knob to the lock position.
Another conventional system disclosed in Japanese Patent Laid-open Publication (Heisei)10-153025 is provided in which a transmission antenna for detecting the approaching of an object into a middle-sized area around a vehicle is mounted on the vehicle in addition to an antenna for transmitting the response demand signal. Upon detecting the approaching of the object or a driver into the middle-sized area, the vehicle releases the response demand signal with a small-sized predetermined communication area and, when receiving a response signal to the response demand signal from the entry key of the right driver, unlock the door. Also, a second transmitting means having a greater communication area is provided for locking the door. The door is thus locked when the communication to the entry key with the second transmitting means is disabled.
According to the conventional systems, when the communication area for the response demand signal is set to be wide enough to detect the driver approaching into the area of the vehicle at an earlier occasion, the door(s) can be unlocked positively before the driver reaches the vehicle. This eliminates the need of the door being unlocked by the driver or user and provides the ease of getting in the vehicle with operating only a door outer handle, hence improving the utility.
However, as the communication area is wide, the locking of the door will be carried out only when the user departs further from the vehicle, hence causing the user to confirm the door locking (through listening to the sound of the door locking mechanism or viewing the shift of the inside door lock knob to the lock position) with much difficulty. Also, while the user with the entry key walks about or pursues a job (e.g. ordering throughout the trunk room), the door locking is not performed and it may fail to protect articles in the vehicle from a thief.
In particular, when the user with the entry key is departing from the vehicle, its back is often turned to the vehicle. The wider the predetermined communication area, the longer the period of the door remaining unlocked is extended and thus the higher the risk of being thieved will be increased. Also, the wider communication area requires a higher level of power for transmitting the response demand signal and the power consumption will be soared up drawing more power from the battery.
For compensation, a modification is proposed such as disclosed in Japanese Patent Laid-open Publication (Heisei) 10-25939, where the communication area is reduced (about one meter in radius) allowing the response demand signal to be not received in a shorter distance from the door thus to lock the door. This permits the door locking to be easily confirmed, the ID code (ID number) to be hardly intercepted, and the power for signal transmission to be minimized, hence lowering the power consumption.
However, the above modification will hardly ensure the unlocking of the door. It is common in the art for minimizing the power consumption for transmitting the response demand signal that the response demand signal from the vehicle is usually transmitted intermittently. With the wider communication area, the user moving in the wider area is able to communicate with the vehicle, even if the response demand signal is transmitted with longer intermission period. Accordingly, the door is surely unlocked before the user arrives at the vehicle.
With the smaller communication area, however, when the user rushes to the vehicle in less time through the communication area, the communication between the vehicle-mounted transmitter and the entry key may not be completed until the user arrives at the vehicle. This causes the door to remain locked and its door outer handle may have to be operated a number of times without success. As a result, the entry key system will be lost in commercial value. As a further modification, the period of the intermittent transmission of the response demand signal may be shortened. This will however increase the power consumption and cause more power be drawn from the battery.
On the other hand, the conventional system disclosed in the above-mentioned Japanese Patent Laid-open Publication (Heisei)10-153025 allows the power for transmitting the response demand signal to be possibly decreased, but it requires the extra transmission antenna for detecting the invading of an object, hence increasing the complexity of the overall arrangement and thus the cost of the system. Also, the power consumption will be increased by the additional equipment. Moreover, the above system transmits the response demand signal even when any other personal or creature than the right entry key (user) advances close to the vehicle, hence requiring more improvement for the power consumption. Since the communication area is too small to examine whether the entry key is right or not as required before accepting the unlocking, the door may remain not unlocked when the user or driver rushes to and arrives at the vehicle. This will result in the misconduct of the automatic unlocking function.